CN110529154A - Prefabricated assembled space grid structure and its construction method for tunnel support - Google Patents

Abstract

The invention provides a prefabricated assembled space grid structure and a construction method for tunnel support. The prefabricated space grid support structure includes at least two prefabricated grid support components, and the grid support components are connected by connecting members to form a closed support structure with the same section shape as the support tunnel section; During construction, the internal force parameters of the tunnel support structure are calculated according to the parameter settings of the tunnel support structure and the tunnel model, and the final construction parameter values of the tunnel support structure are obtained, and the prefabricated space grid support for each ring is prepared. After the tunnel is excavated, the prefabricated grid support components are quickly assembled in the completed excavation section to form a tunnel support closed loop, and the multi-ring grid components are assembled before spraying concrete. The structure of the present invention is simple, easy to assemble, without spraying concrete, relying on the grid structure itself to bear all the tunnel loads, improving construction efficiency.

Description

Prefabricated assembled space grid structure and its construction method for tunnel support

technical field

The invention belongs to the technical field of tunnel engineering construction, and in particular relates to a prefabricated assembly space grid structure for tunnel support and a construction method thereof.

Background technique

Due to the complex and changeable terrain and geological conditions, tunnel engineering construction is prone to disasters of different degrees, resulting in deformation of the tunnel support structure, which threatens the stability of the tunnel to varying degrees, and seriously fails to meet the requirements of the designed lining section, affecting the safe construction of the tunnel. In particular, it brings great difficulty to the construction of tunnels with large spans, complex structures, and strict deformation requirements. At present, the traditional primary support structures of tunnels include anchor shotcrete structures, grid supports, reinforced concrete support structures, etc., but the existing support structures cannot meet their requirements in terms of bearing capacity and support time. Taking the most common grid support structure as an example, the grid support structure is based on the joint action of grid steel frame, section steel steel frame, spray mix, anchor rod and steel mesh. 0.5～1.5m/trunk. Due to its discreteness along the longitudinal direction and the weak bearing capacity of the grid steel frame itself, the ability of the steel frame to bear the load of the surrounding rock is weak before the shotcrete, and the next process must be carried out after the shotcrete, which will cause Extend the construction period and reduce the construction efficiency of the support structure.

With the development of component prefabrication and assembly technology, the prefabrication and assembly of support structures in tunnel construction has gradually become inevitable, which is the main measure that can improve engineering quality and construction speed and reduce costs. Tunnel construction by shield method is a typical representative of prefabricated lining support. However, due to the high construction cost of shield method tunnels, tunnels constructed by mining methods still account for a considerable proportion. However, for the prefabrication of tunnel support structures by mining methods There is less research on assembly technology. At present, the most commonly used support system for mining tunnels is a combined support system consisting of shotcrete, anchor rods, and steel arches. The commonly used steel arches have greater support strength and stiffness, which can enhance the initial support structure. , but the traditional steel arch frame vertical connection reinforcement and locking feet are welded to the steel frame, the construction speed is slow, and it does not meet the requirements of "early closure" in tunnel construction. The on-site overhead welding operation space is narrow and the quality can be guaranteed. , although the steel arch support technology is mature, it is prone to weak axis distortion and instability due to low lateral stiffness. On the premise of satisfying safety and reliability, it is very necessary to develop a prefabricated assembled support structure for reducing the alternate operation time of each process and improving construction efficiency by referring to the current tunnel section shield segment assembly technology.

For the space grid structure, as a space bar structure, it has the characteristics of three-dimensional force and can bear the action of all directions, and the grid structure is generally a high-order hyperstatic structure. If a bar fails locally, only The number of times of super-static indetermination is one less, the internal force can be readjusted, and the entire structure generally does not fail, and has a high safety reserve. Due to its good integrity, good stability, and high spatial rigidity, it can effectively withstand asymmetric loads, concentrated loads and dynamic loads, and has good seismic performance. Its space grid structure has been widely used in the roofs of gymnasiums, theaters, exhibition halls, waiting halls, stadium stand awnings, hangars, two-way large column spacing workshops and other buildings. However, the space grid structure has a large number of rods that meet at the nodes, and the fabrication and installation are more complicated than the plane structure. In addition, the particularity of the tunnel support structure, the limitation of the construction space and the calculation of the bearing capacity of the tunnel support As well as the limitation of requirements, the space grid structure has not been applied to tunnel construction at present.

Contents of the invention

Aiming at the problems of long construction time and insufficient bearing capacity of the traditional support type, the present invention proposes a prefabricated space grid structure suitable for tunnel support and its construction method. The support structure fully utilizes the space grid structure Good mechanical performance and quick assembly construction convenience can ensure the safety of tunnel construction and improve construction efficiency.

The present invention provides a prefabricated space grid structure for tunnel support, characterized in that: the prefabricated space grid support structure includes at least two prefabricated grid support components, each grid The two ends of the frame support member are respectively provided with connection members connected to the adjacent grid support members, and at least two grid support members are connected from the beginning to the end through the connection members to form a closed support structure with the same section shape as the support tunnel ;Each grid support component is a grid support structure composed of upper chords, lower chords and webs. The upper chords form the soil-facing mesh surface that the grid support components contact with the inner wall of the tunnel, and the lower chords form a grid On the back soil mesh surface of the support member, the web members are connected between the upper chord and the lower chord, and are separated between the upper chord and the lower chord to form multiple grid units. The surface is provided with a metal mesh.

The preferred technical solution of the present invention: the soil-facing and back-soil surfaces of the mesh unit of the grid support member are triangular, square, rectangular, pentagonal or hexagonal, and the facade is triangular.

The preferred technical solution of the present invention: the grid support member is a grid support frame composed of a plurality of triangular pyramids, a plurality of quadrangular pyramids or a plurality of hexagonal pyramids.

The preferred technical solution of the present invention: the upper chord and the lower chord of the grid support member are made of any one or several rods of steel pipe, section steel, steel bar, and concrete filled steel tube through welding or direct bending or through connecting pieces The arc-shaped rod body is connected; and the web is connected between the upper chord and the lower chord by welding or connecting pieces to form an arc-shaped grid structure. The web is any one of steel pipe, section steel, steel bar, and steel tube concrete or several rods.

The preferred technical solution of the present invention: the connecting members are matching mortise joints or sleeve connectors or buckle connectors or plug-in or welding connectors, each connecting member is matched with the first connector and The second connectors are respectively arranged at the butt joints of two adjacent network frame support members, and the connection members at both ends of each network frame support member are also matched with each other; at least two network frame support members pass through the first The connecting piece and the second connecting piece are spliced or welded or spliced and welded to form a circular, rectangular, horseshoe or polygonal closed support structure with the same section shape as the section of the support tunnel.

A construction method for a prefabricated space grid structure for tunnel support provided by the present invention is characterized in that it includes at least two rings of the prefabricated space grid support structure in any one of claims 1 to 5 , the specific construction steps are as follows:

(1) Obtain the parameter setting values and the tunnel model of the tunnel support structure; and calculate the bearing load and the elasticity of the equivalent space shell of the tunnel support structure according to the parameter item setting values and the tunnel model Modulus; using the bearing load and the elastic modulus as input of the finite element algorithm to calculate the internal force parameters of the tunnel support structure, and verify the safety of the tunnel support structure according to the internal force parameters, Obtain corresponding verification results, and finally adjust the value of the parameter item according to the verification results to obtain the construction parameter values of the final tunnel support structure;

(2) According to the construction parameter value of the tunnel support structure calculated in step (1), determine the segments of the prefabricated space grid support structure for each ring, and select the appropriate rods according to the segmentation conditions in the factory or On-site fabrication of the single-block grid support components of the prefabricated space grid support structure for each ring and the connectors of the grid support components;

(3) After the excavation of the tunnel, quickly assemble the prefabricated single grid support components in the completed excavation section to form a tunnel support closed loop, and the adjacent two grid support components directly pass through the connectors at their ends Quick connection, its connectors include matching mortise connectors or sleeve connectors or buckle connectors or buckle connections or plug-in connectors, the connectors are directly prefabricated according to the grid support components and then welded on the grid support components. the ends of the guard members;

(4) Continue to excavate the tunnel, and assemble the next ring prefabricated space grid support structure in the excavation section, and the space grid support structure of the adjacent two rings can be lapped with vertically connected steel bars;

(5) According to the actual situation of the project, after the assembly of the multi-ring grid components is completed, spray or pour concrete to form a supporting structure.

The preferred technical solution of the present invention: the parameters of the tunnel support structure in the step (1) include the longitudinal support length of the monolithic prefabricated space grid support structure, the longitudinal section rod body of the tunnel support structure per linear meter The number of roots, the thickness of the initial support, the material thickness of the rod body, the diameter of the connector, the circumferential spacing of the connector, the material of the rod and the connector, the geometric dimensions of the rod and the connector, or any number of parameters item parameter.

The preferred technical solution of the present invention: the bearing load of the tunnel support structure calculated in the step (1) includes the self-weight load of the tunnel support structure and the external load of the tunnel support structure;

Wherein, the self-weight load f of the tunnel support structure is calculated by formula ①:

f＝γ ₁ bh ₁ ; ①

In formula ①, _γ1 represents the concrete weight of the tunnel support structure, b represents the longitudinal width of the calculation unit, and _h1 represents the thickness of the tunnel support structure;

The external load of the tunnel support structure includes the calculation of at least one of the formation resistance borne by the tunnel support structure and the surrounding rock pressure borne by the tunnel support structure; wherein, the surrounding rock pressure borne by the tunnel support structure Including the vertical uniform pressure and horizontal uniform pressure of the surrounding rock borne by the tunnel support structure;

After the calculation of the surrounding rock pressure borne by the tunnel support structure is completed, the surrounding rock pressure is adjusted according to the load factor, wherein the load factor is the ratio of the load value passed in trial calculation to the maximum load value.

The preferred technical solution of the present invention: the calculation process of the formation resistance borne by the tunnel support structure is as follows:

(1) adopt Winkel assumption algorithm, calculate the stratum resistance coefficient of described tunnel model;

(2) Calculate the stratum resistance borne by the tunnel support structure according to the stratum resistance coefficient by the chain rod method.

The preferred technical scheme of the present invention:

In the case where the tunnel model is a deep buried tunnel:

The surrounding rock vertical uniform pressure q borne by the tunnel support structure is calculated by the following formula ②,

q＝γ ₂ h _q ②

In formula ②, h _q = first constant × 2 ^S-1 w, w = second constant + i(B- third constant); γ ₂ represents the weight of the surrounding rock, h _q represents the calculated height of the collapsed arch of the surrounding rock, S represents the grade of surrounding rock, w represents the width influence coefficient, B represents the width of tunnel excavation, and i represents the increase or decrease rate of surrounding rock pressure per unit length increase;

The horizontal evenly distributed pressure of the surrounding rock that the tunnel support structure bears is the product of the vertical uniform pressure q of the surrounding rock and a specific coefficient borne by the above-mentioned calculated tunnel support structure; wherein, the value of the specific coefficient is the same as that of the surrounding rock level dependent.

The preferred technical scheme of the present invention:

In the case where the tunnel model is a shallow buried tunnel:

The surrounding rock vertical uniform pressure q borne by the tunnel support structure is calculated by formula ③,

in,

γ ₂ represents the weight of the surrounding rock, h ₂ represents the height of the tunnel top from the ground, λ represents the lateral pressure coefficient, θ represents the friction angle on both sides of the tunnel top, B represents the tunnel excavation width, β represents the rupture angle at the maximum thrust, Indicates the calculated friction angle of the surrounding rock;

The surrounding rock horizontal and evenly distributed pressure e _i borne by the tunnel support structure is calculated by formula ④,

e _i =γ ₂ h _i λ④

Among them, γ ₂ represents the weight of the surrounding rock, h _i represents the distance from any point on the inside and outside of the tunnel to the ground, and λ represents the lateral pressure coefficient.

The parameters of the tunnel support structure in the step (1) include the longitudinal support length of the monolithic prefabricated space grid support structure, the number of rods in the longitudinal section of the tunnel support structure per linear meter, and the thickness of the initial support , the material thickness of the rod body, the diameter of the connector, the circumferential spacing of the connector, the material of the rod and the connector, the geometric dimensions of the rod and the connector, all or any of several parameters, among which the connection of the rod Form, member material, geometrical dimensions (length, diameter or thickness, etc.) Material and geometrical dimensions of connecting members

Beneficial effects of the present invention:

(1) The support structure in the present invention takes full advantage of the good stress performance of the space grid structure and the convenience of quick assembly, and changes the traditional steel arch frame and other "line support" into "surface support" , to improve the safety and stability of the tunnel;

(2) The prefabricated space grid support structure in the present invention does not need sprayed concrete, and can bear all the tunnel loads by relying on the grid structure itself, which can be assembled quickly and can be carried out after multiple excavation and assembly cycles. Shotcrete reduces the alternation of construction procedures, improves construction efficiency, and ensures the safety of tunnel construction, especially for tunnel excavation sections with complex geology and strict deformation control;

(3) The space grid support structure in the present invention is formed by connecting multiple arc-shaped support structures through quick assembly joints. The arc-shaped support structures can be directly processed in advance or on-site according to the tunnel parameters, and then quickly assembled Forming an overall ring structure avoids problems such as slow tunnel construction and difficult quality assurance caused by welding, and improves construction efficiency;

(4) The space grid support structure in the present invention is made up of a plurality of pyramid structures, wherein one side of each pyramid structure is planar, and the other side is point-like, and the surface and the point are connected by a plurality of pull rods, Under the action of nodal load, each rod mainly bears axial tension and pressure, which can give full play to the strength of the material. Multiple pyramid parts are regularly combined together, which has good integrity, good stability, and large space rigidity. Effectively withstand asymmetric loads, concentrated loads and dynamic loads, and have good seismic performance;

(5) In the present invention, in the construction process, the parameters of the grid support structure are calculated and designed in advance for the required bearing capacity of the tunnel before the shotcrete, so as to ensure that the designed support structure can meet the construction safety and ensure the prefabricated support The structure can provide a large bearing capacity before spraying concrete, and can realize the next process without spraying concrete within a certain working range, which improves the construction efficiency.

(6) The combination of the space grid structure in the present invention is regular, a large number of nodes and rods have the same shape and size, and the specifications of the rods and nodes are less, which is convenient for production and high in product quality.

The present invention can complete the assembly of multi-ring network frame components according to the actual situation and then spray concrete. The supporting components in the structure and construction method are factory-prefabricated, which is convenient for production and controllable in quality. The grid structure itself can bear all the tunnel loads, greatly reducing the alternating time of each process, enabling rapid construction of tunnel support and improving construction efficiency.

Description of drawings

Fig. 1 is the structural representation of the prefabricated assembled space grid support structure of the present invention;

Fig. 2 is the structural representation of grid support member among the present invention;

Fig. 3 is the splicing schematic diagram of grid support member among the present invention;

4a to 4e are structural schematic diagrams of different connecting members in the present invention;

Fig. 5 is a schematic plan view of the grid support member of the present invention;

Fig. 6 is a schematic cross-sectional view of a grid support member of the present invention;

Figures 7a to 7c are structural schematic diagrams of different grid units of the grid support member;

8a to 8c are schematic diagrams of the assembly of the grid units in FIGS. 7a to 7c, respectively.

Fig. 9 is a schematic diagram of the support width and distance of the grid structure;

Fig. 10 is a schematic diagram of the construction state of the present invention.

In the figure: 1—grid support member, 2—tunnel to be supported, 3—upper chord, 4—lower chord, 5—web member, 6—metal mesh, 7—connecting member, 7-1—first connection 7-2—the second connecting piece, 8—concrete lining, a—the width of the grid support member, b—the distance between two adjacent ring grid support structures.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments. Accompanying drawings 1 to 8 are drawings of embodiments, drawn in a simplified manner, and are only used for the purpose of clearly and concisely illustrating embodiments of the present invention. The following technical solutions shown in the drawings are specific solutions of the embodiments of the present invention, and are not intended to limit the scope of the claimed invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

In the description of the present invention, it should be understood that the orientations or positional relationships indicated by the terms "upper", "lower", "inner", "outer", "left", "right" etc. are based on those shown in the accompanying drawings. Orientation or positional relationship, or the orientation or positional relationship that is usually placed when the product of the invention is used, or the orientation or positional relationship that is commonly understood by those skilled in the art, is only for the convenience of describing the present invention and simplifying the description, rather than indicating or It should not be construed as limiting the invention by implying that a referenced device or element must have a particular orientation, be constructed, and operate in a particular orientation.

As shown in Figures 1 to 6, a prefabricated space grid structure for tunnel support provided by the patent of the present invention specifically includes at least two prefabricated grid support components 1, each grid support The two ends of the member 1 are respectively provided with connecting members 7 connected to the adjacent grid support members 1, and the connecting members 7 are mutually matching mortise joints (as shown in Figures 4a and 4b) or sleeve connectors or Snap connectors (as shown in Figure 4c and Figure 4d) or plug-in connectors or buckle connections (as shown in Figure 4e), each connecting member 7 is matched with the first connecting part 7-1 and the second connecting part 7-2 They are respectively arranged at the butt joints of two adjacent network frame support members 1, and the connecting members 7 at both ends of each network frame support member 1 are also matched with each other; at least two network frame support members 1 pass through the first The connecting piece 7-1 and the second connecting piece 7-2 are spliced into a circular, rectangular, horseshoe or polygonal closed support structure with the same section shape as the support tunnel 2 . The prefabricated grid support member 1 is prefabricated in sections according to the shape of the section of the tunnel, and adapted to the shape of the section of the tunnel, and the specific shape assembled is not limited.

In the prefabricated space grid support structure for tunnel support provided in the present invention, each grid support member 1 is a grid support structure composed of upper chord 3, lower chord 4 and web 5, and the upper chord Rods 3 form the soil-facing mesh surface where the grid support member 1 contacts the inner wall of the tunnel 6, the lower chord 4 forms the back soil mesh surface of the grid support member 1, and the web bars 5 are connected between the upper chord 3 and the lower chord 4 , and a plurality of grid units are formed between the upper chord 3 and the lower chord 4 , and a metal mesh 6 is provided on the soil-facing mesh surface of each grid support member 1 . Among them, the soil-facing mesh surface and the soil-back mesh surface of the grid support member 1 respectively form the outer ring structure and the inner ring structure of the whole support, since the rods on the outer ring structure and the inner ring structure are evenly arranged, this can ensure The force on the structure of the outer ring and the structure of the inner ring is even.

In the present invention, the earth-facing surface and the back-soil surface of grid support component 1 grid unit are triangles, squares, rectangles, pentagons or hexagons. The smallest shape unit surrounded by the rods in the soil mesh surface through the webs 5 is a triangle, and the support strength of the prefabricated components can be further improved by the triangular stable structure. The upper chord 3 and the lower chord 4 of the grid support member 1 are arcs formed by welding or directly bending or connecting any one or several rods in steel pipe, section steel, steel bar and steel tube concrete. shaped bar body; and between the upper chord 3 and the lower chord 4, the web 5 is connected by welding or a connector to form an arc-shaped grid structure, and the web 5 is any one of steel pipe, section steel, steel bar, steel pipe concrete or Several rods.

The grid supporting member 1 provided in the present invention is a grid support frame composed of a plurality of triangular pyramids or a plurality of quadrangular pyramids or a plurality of hexagonal pyramids. The triangular pyramids are shown in Figures 7a and 8a. The triangular bottom of the pyramid is connected into a curved surface, which is the earth-facing surface of the grid support member 1, and the three support rods that form the triangular bottom of the triangular pyramid are the upper chords of the grid support member 1, and the adjacent two triangular pyramids The apex of the cone is connected as a whole through the inner chord rod 4, and the three support rods forming the triangular pyramid after connection are the web rods of the grid support member 1. As shown in Figures 7b and 8b, the quadrangular pyramid is the same as the triangular pyramid, and its quadrangular bottom surface is connected to a curved surface. This plane is the earth-facing surface of the grid support member 1. The upper chord of the grid support member 1, the cone tips of two adjacent quadrangular pyramids are connected as a whole through the inner chord 4, and the four support rods that form the quadrangular pyramid cone after connection are the webs of the grid support member 1 . As shown in Figures 7c and 8c, the hexagonal pyramid has a hexagonal bottom connected to form a curved surface, which is the soil-facing surface of the grid support member 1, and the six support rods that form the hexagonal bottom of the hexagonal pyramid are the grid support members. The upper chord of 1, the cone tips of two adjacent hexagonal pyramids are connected as a whole through the inner chord 4, and after the connection, the six support rods forming the hexagonal pyramid are the webs of the grid support member 1.

The present invention will be further described below in conjunction with the embodiments. The calculation of the parameter value determination scheme in the embodiments of the present invention can be realized by various computer languages, for example, the object-oriented programming language Java and the literal translation script language JavaScript.

The embodiment provides a construction method for a prefabricated space grid structure used for tunnel support. The spacing b of the ring grid support structure can be taken as 0 according to the actual situation, as shown in Figure 1, the perimeter of the tunnel section Among them, n is the segment number of the tunnel section member, Li is the length of the i-th section member, and the connecting member 7 on the grid support member 1 is a mortise joint joint that can be spliced with each other. The specific construction steps of the support structure are as follows:

(1) Determine the construction parameter values of the tunnel support structure:

a. Obtain the parameter settings and tunnel model of the tunnel support structure; its parameter items include but not limited to: the longitudinal support length of each space grid support structure, the longitudinal length of each space grid support structure The number of steel bars (pipes) in the section (one side), the thickness of the initial support, the material thickness of the rod body (such as the diameter of the steel bar, the wall thickness of the steel pipe), the diameter of the connecting piece, and the circumferential spacing of the connecting piece, etc. The setting values of these parameters can be parameter experience values or design values. The tunnel model of the embodiment of the present invention is used to simulate the actual tunnel situation, and is related to tunnel engineering geology, hydrogeological conditions, and existing tunnel design and construction experience. Parameters such as the shape of the tunnel section;

b. According to the set values of the parameter items and the tunnel model, calculate the bearing load of the tunnel support structure and the elastic modulus of the equivalent space shell. The bearing load mainly includes self-weight load and external load, and the external load mainly includes: Stratum resistance and surrounding rock pressure, etc.; the tunnel support structure can be equivalent to a space shell structure, and the elastic modulus of the equivalent space shell is calculated by using the set values of each parameter item of the tunnel support structure. It can better simulate the tunnel support structure, and the calculated elastic modulus can be equivalent to the elastic modulus of the tunnel support structure as a whole;

c. The bearing load and elastic modulus are used as the input of the finite element algorithm to calculate the internal force parameters of the tunnel support structure. The internal force parameters include: bending moment, axial force (axial force) and shear force, etc.; according to the internal force parameters, Verify the safety of the tunnel support structure and obtain the corresponding verification results. According to the verification results, adjust the values of the parameter items. Security parameter item. If the verification result indicates that the safety requirements are met, and the safety requirements are exceeded, it is necessary to adjust the value of each parameter item to continue verification, so as to save materials and reduce costs;

d. Finally, according to the verification result, adjust the value of the parameter item to obtain the construction parameter value of the final tunnel support structure;

(2) According to the construction parameter values of the tunnel support structure calculated in step (1), determine the subsections of the prefabricated space grid support structure for each ring, and select appropriate rods and connectors, according to the subsections Circumstances Manufacture the single-block grid support components of each ring prefabricated space grid support structure and the connectors of the grid support components in the factory or on site;

(3) After the excavation of the tunnel, quickly assemble the prefabricated single grid support components in the completed excavation section to form a tunnel support closed loop, and the adjacent two grid support components are connected by connecting components 7, and the The component 7 includes matching mortise joints or sleeve joints or buckle joints or buckle joints or plug-in joints. When the connecting member is a tenon joint, as shown in Figure 4a and Figure 4b, the composition The first connecting piece 7-1 and the second connecting piece 7-2 of the connecting member 7 are protrusions and grooves that match each other. When connecting, it is only necessary to directly butt the two parts, and the protrusions are embedded in the grooves of each other. It can be clamped; when the connecting member is a buckle connector, as shown in Figure 4c and Figure 4d, it includes a first connecting member with a bayonet and a second connecting member with a lock hole, and the second connecting member is inserted correspondingly In the first connecting member, and locked by a lock; when the connecting member is a disc buckle connection, as shown in Figure 4e, the first connecting member is provided with a disc-shaped opening, and the second connecting member is connected to the first connecting member. After the components are clamped, they are locked by the locking block; the connecting member 7 in the embodiment is directly prefabricated according to the grid support component and then welded to the end of the grid support component; when the grid support component is installed, the present invention The electric multifunctional arch installation machine is used to replace the traditional vertical trolley, and the automatic installation is carried out through the operation methods such as lifting of the multifunctional arch installation trolley and arm grabbing. The multifunctional arch installation machine has the multifunctional arch installation trolley. The automatic walking and automatic positioning system, combined with the arm and the hanging basket, realizes the all-round movement of the multifunctional arch trolley, the precise hoisting of the arch, and the completion of the construction process of the arch installation. Its overall movement is fast and convenient, and its applicability is wide. The frame moves in all directions and can be positioned at any position. The whole equipment is controlled by a safe hydraulic and electric control system;

(4) Continue to excavate the tunnel, and continue to use the multifunctional arch installation machine to assemble the next ring prefabricated space grid support structure in the excavation section; the adjacent two ring space grid support structures can use longitudinal connection steel bars overlap;

(5) According to the actual situation of the project, after completing the single-ring prefabricated space grid support structure or completing several ring prefabricated space grid support structures, spray or pour concrete on the grid support structure, and place The prefabricated space grid support structure is wrapped to form a lining structure; due to the strong rigidity of the space grid support structure, it can bear the relaxation load of the surrounding rock during construction, and the next process can be carried out without spraying concrete immediately. During the excavation progress, within a certain distance from the face of the tunnel, sprayed concrete is delayed, and only the space grid support structure can be used as the bearing structure for the initial support.

In the embodiment of the present invention, as shown in Figure 10, at least two space grid support structures are required, and the longitudinal support length L of each space grid support structure, the space grid support per linear meter The number of steel bars (pipes) in the longitudinal section of the structure (one side) n, the thickness h of the primary support and other structural parameters, these parameter items can be taken as industry experience values. For other parameter items, a set value can be assumed, such as the material thickness of the rod body, for structural mechanics analysis to check whether the structural safety factor meets the requirements. Through the trial calculation of these parameter items, the value of the parameter item that meets the security requirements is obtained.

In the above embodiment, the self-weight load and external load are determined as the bearing load of the tunnel support structure, and the calculation process for the bearing load is specifically as follows:

1. Calculation of self-weight load

Among them, according to the setting value of the parameter item, the steps of calculating the self-weight load of the tunnel support structure include: using the formula ① to calculate the self-weight load f of the tunnel support structure; where, the formula ① is:

f=γ ₁ bh ₁ ;

Among them, γ ₁ represents the concrete weight of the tunnel support structure, b represents the longitudinal width of the calculation unit, and h ₁ represents the thickness of the tunnel support structure.

2. Calculation of external load

According to the tunnel model, the step of calculating the external load of the tunnel support structure includes at least one of the following: according to the tunnel model, calculating the formation resistance borne by the tunnel support structure; according to the type of the tunnel model, calculating the resistance of the tunnel support structure Surrounding rock pressure.

1. Calculation of formation resistance

According to the tunnel model, the steps of calculating the ground resistance of the tunnel support structure include: using the Winkel assumption algorithm to calculate the ground resistance coefficient of the tunnel model; using the chain rod method to calculate the ground resistance of the tunnel support structure according to the ground resistance coefficient ground resistance. Specifically, in the chain rod method, formation resistance is simulated by formation springs. The stratum resistance coefficient is determined according to the soil layer conditions and calculated according to the Winkel assumption. In the calculation, the spring in tension is eliminated.

2. Calculation of surrounding rock pressure

According to the type of the tunnel model, the step of calculating the surrounding rock pressure borne by the tunnel support structure includes: according to the type of the tunnel model, respectively calculating the vertical uniform pressure and the horizontal uniform pressure of the surrounding rock borne by the tunnel support structure. Among them, the calculation methods of vertical uniform pressure and horizontal uniform pressure under the tunnel model are different. The type of tunnel model is different, the calculation method of vertical uniform pressure is different, and the calculation method of horizontal uniform pressure is also different. In the following, this embodiment will be further described in combination with the calculation of surrounding rock pressure for deep tunnels and shallow tunnels.

2-1. Conditions of deep buried tunnels

The case of a deeply buried tunnel refers to the case where the distance between the centerline, top or bottom of the tunnel and the ground surface exceeds a certain value, and in this embodiment refers to the case other than the case of a shallow buried tunnel. For the calculation of vertical uniform pressure: when the tunnel model is a deep tunnel, formula ② is used to calculate the vertical uniform pressure q of the surrounding rock borne by the tunnel support structure (the unit can be kPa); among them, formula ② is :

q＝γ ₂ h _q

Wherein, h _q =first constant×2 ^S-1 w, w=second constant+i(B-third constant);

Among them, γ ₂ represents the weight of the surrounding rock (the unit can be kN/m ³ ), h _q represents the calculated height of the surrounding rock collapse arch (the unit can be m), S represents the grade of the surrounding rock, w represents the width influence coefficient, and B represents the tunnel Excavation width (unit can be m), i represents the rate of increase or decrease of surrounding rock pressure per unit length increase.

Optionally, the first constant may be 0.45, the second constant may be 1, and the third constant may be 5. Correspondingly, h _q =0.45×2 ^S-1 w, w=1+i(B-5). Among them, when B<5m, take i=0.2, and when B≥5m, take i=0.1.

For the calculation of horizontal uniform pressure: when the tunnel model is a deep tunnel, the product of the vertical uniform pressure of the surrounding rock borne by the tunnel support structure and a specific coefficient is determined as the horizontal uniform pressure of the surrounding rock borne by the tunnel support structure Distribution pressure, where the value of a certain coefficient is related to the grade of the surrounding rock. For example, the horizontal uniform pressure in this case can be determined from Table 1 below:

Table 1

Surrounding rock level Ⅰ～Ⅱ III IV Ⅴ Horizontal uniform pressure 0 <0.15q (0.15～0.30)q (0.30～0.50)q

2-2. Conditions of deep buried tunnels

Shallow buried tunnel refers to the case where the distance between the centerline, top or bottom of the tunnel and the ground surface is lower than a certain value, such as the case where the buried depth of the tunnel is greater than h _q and less than 2.5h _q .

For the calculation of vertical uniform pressure: when the tunnel model is a shallow tunnel, formula ③ is used to calculate the vertical uniform pressure q of the surrounding rock borne by the tunnel support structure; among them, formula ③ is:

in,

γ ₂ represents the weight of the surrounding rock (the unit can be kN/m ³ ), h ₂ represents the height of the tunnel top from the ground (the unit can be m), λ represents the lateral pressure coefficient, and θ represents the friction angle on both sides of the tunnel top (the unit can be is °, generally take the empirical value), B represents the tunnel excavation width or the tunnel span (the unit can be m), β represents the rupture angle at the maximum thrust (the unit can be °), Indicates the calculated friction angle of the surrounding rock (the unit can be °).

Optionally, the fourth constant may be 1, the fifth constant may be 1, and the sixth constant may be 1. Correspondingly,

For the calculation of the horizontal uniform pressure: when the tunnel model is a shallow tunnel, the first formula ④ is used to calculate the horizontal uniform pressure e _i of the surrounding rock borne by the tunnel support structure; among them, the formula ④ is:

e _i =γ ₂ h _i λ

Among them, γ ₂ represents the weight of the surrounding rock (the unit can be kN/m ³ ), h _i represents the distance from any point on the inside and outside of the tunnel to the ground (the unit can be m), and λ represents the lateral pressure coefficient.

Furthermore, the surrounding rock pressure calculated above is the maximum relaxation load borne by the tunnel lining. However, considering the supporting effects of the surrounding rock in front of the tunnel face, the primary support at the rear and the secondary lining, there is a certain spatial effect. The actual construction During the process, the space grid support structure will not bear such a large load, so in the design, the above load is reduced. Specifically, after the surrounding rock pressure is calculated, the surrounding rock pressure is adjusted according to the load coefficient, wherein the load coefficient is the ratio of the load value passed through the trial calculation to the maximum load value. For example, assuming that the surrounding rock load is q, q=μq', among them, μ represents the load factor, which is the ratio of the load value passed in the trial calculation to the maximum load value, and q' represents the effect on the tunnel support structure (space grid support slack load on the structure).

It is worth pointing out that in the stage of erecting the space grid support structure and the stage of sprayed concrete, the load acting on the tunnel support structure is adjusted by using different load coefficients μ, so as to obtain the actual force condition of the support structure load.

The calculation methods of bearing loads in different scenarios have been introduced above. The following will further illustrate the example of calculating the elastic modulus of the tunnel support structure in step 1 in combination with the application scenarios.

Specifically, taking the horseshoe-shaped cross-section structural lining of the underground excavation tunnel shown in Figure 1 as an example, the structural force is mainly eccentrically compressed. The supporting structure is equivalent to a space shell structure with a certain thickness.

In the stage of erecting the support structure, EA=E _g (A _g +A' _g ), A=Lh, correspondingly, step 13 includes: using formula ⑤ to calculate the elastic modulus of the equivalent space shell of the tunnel support structure Quantity E; Among them, the formula ⑤ is:

Among them, A _g and A' _g represent the cross-sectional area of the rod body in the tension and compression zone (the unit can be m ² ), E _g represents the material modulus of the rod body, and L represents the weight of a grid support structure in the tunnel support structure. The longitudinal length, h represents the thickness of the equivalent space shell.

Among them, in the case that the rod body is a steel bar, Among them, n represents the number of rods contained in the longitudinal section of the grid support structure of one linear meter, and D represents the diameter of the steel bar.

In the case that the rod body is a steel pipe, n represents the number of rods contained in the longitudinal section of the one-meter grid support structure, D represents the diameter of the steel pipe, and t represents the wall thickness of the steel pipe.

The calculation of the elastic modulus at the erection stage of the steel frame is introduced above. For the shotcrete stage, according to the existing design experience, at this stage, the contribution of the stiffness of the steel to the equivalent stiffness of the section is almost negligible. Therefore, at this stage, the stiffness of the shotcrete can be directly used as the stiffness of the equivalent section.

The calculation of the internal force parameters is based on the calculation results of the above-mentioned bearing load and the elastic modulus of the equivalent space shell. According to the basic principles of elastic mechanics, the problem of solving the internal force of the tunnel section can be simplified as a plane strain problem in the embodiment of the present invention. . Using the finite element method, the internal forces (bending moment M, axial force N and shear force Q) of the support structure in the stage of erecting the steel frame and the stage of sprayed concrete are calculated respectively.

After obtaining the internal force parameters, the safety of the tunnel support structure can be verified based on the internal force parameters. The following embodiments of the present invention will verify the safety in combination with different construction stages, so as to obtain appropriate design values of structural parameters.

In the stage of erecting the space grid support structure, formula ⑥ is used to calculate the corresponding verification result; when the verification result is that the safety factor is greater than or equal to the first value, it is determined that the safety of the tunnel support structure meets the requirements. Assuming that the first value is 2.4, then when K is greater than or equal to 2.4, the value of the parameter item of the tunnel support structure meets the safety requirements; otherwise, perform step 16, adjust the value of the parameter item, and perform the next trial calculation. until a suitable value is obtained.

Among them, the formula ⑥ is: KN=αR _g A, where K represents the safety factor, N represents the axial force, α represents the eccentric influence coefficient of the axial force, R _g represents the tensile and compressive ultimate strength of the material of the grid support structure, A Indicates the cross-sectional area of the equivalent space shell.

Optionally, the eccentric influence coefficient of the axial force is related to the eccentricity of the axial force and the thickness of the equivalent space shell. E.g, Among them, e ₀ represents the eccentricity of the axial force, and h represents the thickness of the equivalent space shell.

After the step of obtaining the verification result, a step of calculating the values of other parameter items may also be included, specifically, verifying the safety of the tunnel support structure according to the internal force parameters, and obtaining corresponding verification results. Then use the formula ⑦ to calculate the structural parameters of the connector; where, the formula ⑦ is:

K represents the safety factor, Q represents the shear force, R _g represents the tensile and compressive ultimate strength of the material of the grid support structure, A _k represents the cross-sectional area of the joint between the connector and the rod body, and l _e represents the beam element selected in the finite element algorithm The length of , θ represents the friction angle on both sides of the top of the tunnel, and c represents the circumferential spacing of the connector. Optionally, the seventh constant can be 0.8, correspondingly,

In this way, through the calculation of the shear strength, the diameter d of the connector and the circumferential spacing c can meet the requirements of the shear strength of the structure.

The safety verification method in the stage of erecting the space grid support structure has been introduced above, and the safety verification method after the shotcrete stage will be further introduced in the following.

After the shotcrete stage, when the height of the concrete compression zone is less than or equal to the threshold value, use formula ⑧ to calculate the corresponding verification result; when the verification result is that the safety factor is greater than or equal to the first value, determine the tunnel support structure Security meets the requirements.

Wherein, formula 8 is:

KNe≤R _w bx(h ₀ -x/2)+R _g A' _g (h ₀ -a')

in,

K represents the safety factor, N represents the axial force, e and e ^' represent the distance from the center of gravity of the bar in the tension and compression zone to the point where the axial force acts, R _w represents the ultimate strength of the concrete bending compressive force, b represents the longitudinal width of the calculation unit, x represents the height of the concrete compression zone (the unit can be m), R _g represents the tensile and compressive ultimate strength of the material of the grid support structure, A _g and A' _g represent the cross-sectional area of the rod in the tension and compression area ( The unit can be m ² ), a, a' represent the shortest distance from the center of gravity of the bar body in the tension and compression zone to the section edge of the equivalent space shell (the unit can be m), h ₀ represents the distance of the equivalent space shell Effective height of the section, h ₀ =ha.

Specifically, in the stress stage after the sprayed concrete stage, the moment of the acting point of the axial force is R _g (A _g eA' _g e')=R _w bx(eh ₀ -x/2), from which Deduced: Among them, R _w represents the concrete bending compressive ultimate strength, x represents the height of the concrete compression zone, R _g , R' _g represents the tensile and compressive strength of the material of the grid support structure, A _g , A' _g Indicates the cross-sectional area of the rod body in the tension and compression area, e, e' represent the distance from the center of gravity of the rod body in the tension and compression area to the point where the axial force acts, a, a' represent the center of gravity of A _g , A' _g to The shortest distance of the section edge of the equivalent space shell, h ₀ represents the effective height of the section of the equivalent space shell.

Correspondingly, assuming that the threshold value is 0.55h ₀ , then when x is less than or equal to 0.55h ₀ , it is a large eccentric compression member, which is calculated according to the eighth formula, that is, KNe≤R _w bx(h ₀ -x/2)+ R _g A' _g (h ₀ - a'), the calculation needs to satisfy x≥2a', if not, that is, when x<2a', calculate according to KNe'≤R _g A _g (h ₀ - a').

After the shotcrete stage, when the height of the concrete compression zone is greater than the threshold value, formula ⑨ is used to calculate the corresponding verification result; when the verification result is that the safety factor is greater than or equal to the first value, the safety of the tunnel support structure is determined sexual satisfaction. Among them, the formula ⑨ is: Among them, K represents the safety factor, N represents the axial force, e represents the distance from the center of gravity of the rod body to the point where the axial force acts, R _a represents the ultimate compressive strength of the concrete, b represents the longitudinal width of the calculation unit, and R _g represents the grid support structure The tensile and compressive ultimate strength of the material, A' _g represents the cross-sectional area of the rod body, a' represents the shortest distance from the center of gravity of the rod body to the section edge of the equivalent space shell, and _h0 represents the effective height of the cross-section of the equivalent space shell.

Correspondingly, assuming that the threshold value is 0.55h ₀ , then when x is greater than 0.55h ₀ , it is a small eccentric compression member, and the section strength is calculated according to the ninth formula, and the eighth constant can be 0.5, namely

The calculation method of the main reinforcement at this construction stage has been introduced above, and the safety factor after reinforcement will be further introduced below:

In this embodiment, it is assumed that the first value is 2.4, that is, when K is greater than or equal to 2.4, it means that the design values of the parameter items of the tunnel support structure meet the safety requirements.

The above is mainly for the design and verification of the value of the parameter item of the rod body in the tunnel support structure. The following will further design and verify the value of the parameter item of the connector with examples.

Specifically, after the step of verifying the safety of the tunnel support structure according to the internal force parameters and obtaining the corresponding verification results, it also includes: using the formula ⑩ to calculate the structural parameters of the connector; where the formula ⑩ is:

K represents the safety factor, Q represents the shear force, R _a represents the ultimate compressive strength of concrete, b represents the longitudinal width of the calculation unit, _h0 represents the effective height of the section of the equivalent space shell, R _g represents the material of the grid support structure A _k represents the cross-sectional area of the joint between the connector and the rod body, l _e represents the length of the beam element selected in the finite element algorithm, θ represents the friction angle on both sides of the tunnel top, and c represents the circumferential direction of the connector spacing. Suppose the ninth constant is 0.07, and the tenth constant is 0.8. Correspondingly, the tenth formula is: According to this formula, the limit value of the circumferential spacing of the connectors meeting the shear resistance requirements can be calculated.

In the embodiment of the present invention, when the verification result is that the safety factor is less than the safety requirement threshold, the value of the parameter item is increased; when the verification result is that the safety factor exceeds the safety requirement threshold and reaches a specific value, the value of the parameter item is decreased ; When the verification result is that the safety factor exceeds the safety requirement threshold and does not reach a specific value, keep the set value of the parameter item unchanged. Taking the safety factor K as an example, assuming that the first value is 2.4, if K<2.4, it means that the current design value of the parameter item of the tunnel support structure is not safe, and it is necessary to increase the design value and recalculate; if K>>2.4 , it shows that the bearing capacity of the tunnel support structure is relatively rich, and it is necessary to reduce the design value of the parameter item and recalculate; when K is slightly greater than 2.4, it indicates that the bearing capacity of the tunnel support structure can meet the requirements and is more economical.

It is worth pointing out that the initial support is used as a temporary structure during the construction period to bear the proportional coefficient of the surrounding rock load. After the secondary lining is installed, its force will be improved. Therefore, there is no need to check and calculate the crack width during the construction period. , but it can be used as a reference indicator when designing. Reinforced concrete tension, bending and eccentric compression members, for eccentric compression members with e ₀ ≤ 0.55h ₀ , the crack width may not be checked. In other cases, calculate the crack width according to the following formula:

Among them, ω _max represents the maximum crack width (the unit can be mm); α represents the characteristic coefficient of component stress of the tunnel support structure, and the tunnel is an eccentric compression member, and α can be 1.9; Indicates the non-uniform coefficient of strain in longitudinal tension steel bars between cracks, when hour, Take 0.2, when hour, Take 0.2, when hour, Take 1.0, for members directly subjected to repeated loads, ρ te is taken as 1.0; ρ _te represents the reinforcement ratio of longitudinal tensile reinforcement calculated according to the effective tensile concrete area, ρ _te =A _s /A _ce , when ρ _te <0.01, ρ _te is taken as 0.01; A _s represents the longitudinal Reinforcement cross-sectional area; A _ce represents the effective tensile concrete cross-sectional area, A _ce = 0.5bh; C _s represents the distance from the outer edge of the outermost longitudinal tension kilogram to the bottom edge of the tension zone (unit can be mm), when C _s When <20, C _s takes 20, when C _s >65, C _s takes 65; d indicates the steel bar diameter (unit can be mm), when using different diameter steel bar, d=4A _s /(γμ), μ Indicates the sum of the perimeter of the cross-section of the longitudinally tensioned steel bar; γ indicates the surface characteristic coefficient of the longitudinally tensioned steel bar, taking 1 for the deformed steel bar and 0.7 for the smooth steel bar; E _s indicates the elastic modulus of the steel bar (the unit can be MPa); σ _s indicates The stress of the longitudinal tensile reinforcement (unit can be MPa), σ _s =N _s (ez)/(A _s z), N _s represents the axial force value calculated according to the load combination, z represents the resultant force point in kilograms to the The distance of the resultant force point in the nip, z=[0.87- 0.12(h ₀ /e) ² ]h ₀ , and z<0.87h ₀ .

Before the construction of the space grid support structure in the present invention, the force of the support structure can be calculated according to the geological conditions of the tunnel through the above calculation process, and the various components of the tunnel support structure can be determined in combination with the assembly capacity of the assembling trolley and the tunnel section size. parameters, and then prefabricated and spliced into a support structure with the same shape as the tunnel section, to realize the parameter design of the support structure that can provide a large bearing capacity before spraying concrete, and ensure that the designed support structure can meet the construction safety requirements. Since the support structure can provide a large bearing capacity before spraying concrete, the next process can be carried out without spraying concrete within a certain working range, which improves the construction efficiency.

While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the appended claims.

Claims (11)

1. The utility model provides a prefabricated assembled space grid structure for tunnel supporting which characterized in that: the prefabricated space net rack supporting structure comprises at least two prefabricated net rack supporting members (1), connecting members (7) connected with adjacent net rack supporting members (1) are respectively arranged at two ends of each net rack supporting member (1), and the at least two net rack supporting members (1) are connected end to end through the connecting members (7) to form a closed supporting structure with the same section as the section of a supporting tunnel (2); each net rack supporting component (1) is a grid supporting structure consisting of an upper chord (3), a lower chord (4) and a web member (5), the upper chord (3) forms an earth-facing net surface of the net rack supporting component (1) contacted with the inner wall of the tunnel (6), the lower chord (4) forms an earth-backing net surface of the net rack supporting component (1), the web member (5) is connected between the upper chord (3) and the lower chord (4) and is separated between the upper chord (3) and the lower chord (4) to form a plurality of grid units, and a metal net (6) is arranged on the earth-facing net surface of each net rack supporting component (1).

2. A prefabricated spatial grid structure for tunnel bracing according to claim 1, wherein: the grid unit soil facing surface and the soil backing surface of the net rack supporting member (1) are triangular, square, rectangular, pentagonal or hexagonal, and the vertical surface is triangular.

3. A prefabricated spatial grid structure for tunnel bracing according to claim 1, wherein: the net rack supporting component (1) is a grid type supporting frame consisting of a plurality of triangular pyramids or a plurality of rectangular pyramids or a plurality of hexagonal pyramids.

4. A prefabricated spatial grid structure for tunnel bracing according to claim 1, wherein: the upper chord (3) and the lower chord (4) of the net rack supporting member (1) are arc-shaped rod bodies formed by welding or directly bending or connecting any one or more of steel pipes, section steel, steel bars and steel pipe concrete or by connecting pieces; and the upper chord member (3) and the lower chord member (4) are connected with the web members (5) through welding or connecting pieces to form an arc-shaped grid structure, and the web members (5) are any one or more of steel pipes, section steel, reinforcing steel bars and steel pipe concrete.

5. A prefabricated spatial grid structure for tunnel bracing according to claim 1, wherein: the connecting members (7) are mutually matched tenon connecting pieces or sleeve connecting pieces or buckle connecting pieces or plug-in or welding connecting pieces, a first connecting piece (7-1) and a second connecting piece (7-2) which are mutually matched with each connecting member (7) are respectively arranged at the butt joint part of two adjacent net rack supporting members (1), and the connecting members (7) at the two ends of each net rack supporting member (1) are also mutually matched; at least two net rack supporting members (1) are connected into an annular, rectangular, horseshoe-shaped or polygonal closed supporting structure with the same cross section as that of the supporting tunnel (2) by adopting a splicing or welding mode or a splicing and welding combined mode through a first connecting piece (7-1) and a second connecting piece (7-2).

6. A construction method of a prefabricated space grid structure for tunnel supporting, wherein the prefabricated space grid structure of any one of claims 1 to 5 comprises at least two rings, and the construction method comprises the following concrete steps:

(1) acquiring various parameter set values and a tunnel model of a tunnel supporting structure; calculating the bearing load of the tunnel supporting structure and the elastic modulus of the equivalent space shell according to the parameter item set value and the tunnel model; taking the bearing load and the elastic modulus as input of a finite element algorithm, calculating an internal force parameter of the tunnel supporting structure, verifying the safety of the tunnel supporting structure according to the internal force parameter to obtain a corresponding verification result, and finally adjusting the value of the parameter item according to the verification result to obtain a final construction parameter value of the tunnel supporting structure;

(2) determining the subsection of each ring of prefabricated assembly type space net rack supporting structure according to the construction parameter values of the tunnel supporting structure calculated in the step (1), and selecting a proper rod piece to manufacture a single net rack supporting member of each ring of prefabricated assembly type space net rack supporting structure and a connecting piece of the net rack supporting member in a factory or on the spot according to the subsection condition;

(3) after the tunnel is excavated, quickly assembling prefabricated single-block net rack supporting members at the finished excavation section to form a tunnel supporting closed ring;

(4) continuously excavating the tunnel, and assembling a next ring of prefabricated assembly type space net rack supporting structure at an excavation section;

(5) according to the actual situation of the engineering, after the single-ring prefabricated assembly type space net rack supporting structure is completed or a plurality of rings of prefabricated assembly type space net rack supporting structures are completed, concrete is sprayed or poured on the net rack supporting structures, and the prefabricated assembly type space net rack supporting structures are wrapped to form a lining structure.

7. The construction method of the prefabricated spatial grid structure for tunnel support according to claim 6, wherein: the parameters of the tunnel supporting structure in the step (1) comprise all or any parameters of the longitudinal supporting length of the single prefabricated assembly type space net rack supporting structure, the number of rod bodies in the longitudinal section of the tunnel supporting structure per linear meter, the thickness of primary support, the material thickness of the rod bodies, the diameter of the connecting piece, the circumferential distance of the connecting piece, the materials of the rod pieces and the connecting piece, and the geometric dimensions of the rod pieces and the connecting piece.

8. The construction method of a prefabricated spatial grid structure for tunnel supporting according to claim 6, wherein the bearing load of the tunnel supporting structure calculated in the step (1) includes a self-weight load of the tunnel supporting structure and an external load of the tunnel supporting structure;

wherein the dead weight f of the tunnel supporting structure is calculated by adopting a formula I

f＝γ₁bh₁； ①

In formula (I), gamma₁Representing the concrete weight of the tunnel supporting structure, b representing the longitudinal width of the calculation unit, h₁Representing the thickness of the tunnel supporting structure;

the external load of the tunnel supporting structure comprises calculation of at least one of stratum resistance borne by the tunnel supporting structure and surrounding rock pressure borne by the tunnel supporting structure; the surrounding rock pressure borne by the tunnel supporting structure comprises surrounding rock vertically-uniformly-distributed pressure and horizontally-uniformly-distributed pressure borne by the tunnel supporting structure;

after the surrounding rock pressure borne by the tunnel supporting structure is calculated, the surrounding rock pressure is adjusted according to a load coefficient, wherein the load coefficient is the ratio of a trial-calculated load value to a maximum load value.

9. The construction method of the prefabricated spatial grid structure for tunnel supporting according to claim 8, wherein the resistance of the tunnel supporting structure to the ground layer is calculated as follows:

(1) calculating a formation resistance coefficient of the tunnel model by adopting a Wenkel assumption algorithm;

(2) and calculating the stratum resistance borne by the tunnel supporting structure according to the stratum resistance coefficient by a chain rod method.

10. The construction method of a prefabricated spatial grid structure for tunnel bracing according to claim 8, wherein in case that the tunnel model is a deep-buried tunnel:

the vertical uniform pressure q of the surrounding rock born by the tunnel supporting structure is calculated by adopting the following formula II,

q＝γ₂h_q ②

formula II, h_qFirst constant x 2^S-1w, w ═ a second constant + i (B — a third constant); gamma ray₂Indicates the weight of the surrounding rock, h_qThe calculation height of the collapse arch of the surrounding rock is represented, S represents the surrounding rock level, w represents the width influence coefficient, B represents the tunnel excavation width, and i represents the surrounding rock pressure increase and decrease rate of each increased unit length;

the horizontal uniform distribution pressure of the surrounding rock borne by the tunnel supporting structure is the product of the calculated vertical uniform distribution pressure q of the surrounding rock borne by the tunnel supporting structure and a specific coefficient; wherein the value of the specific coefficient is related to a surrounding rock level.

11. The construction method of a prefabricated spatial grid structure for tunnel bracing according to claim 8, wherein in case that the tunnel model is a shallow tunnel:

the vertical uniform pressure q of the surrounding rock born by the tunnel supporting structure is obtained by calculation by adopting a formula (III),

wherein,

γ₂indicates the weight of the surrounding rock, h₂Indicating the height of the tunnel roof from the ground, λ the lateral pressure coefficient, θ the tunnel roofThe friction angle at both sides, B represents the tunnel excavation width, β represents the breakout angle at maximum thrust,representing the calculated friction angle of the surrounding rock;

surrounding rock horizontal uniform distribution pressure e borne by tunnel supporting structure_iIs obtained by calculation by adopting a formula (IV),

e_i＝γ₂h_iλ ④

wherein, γ₂Indicates the weight of the surrounding rock, h_iThe distance between any point inside and outside the tunnel and the ground is shown, and the lambda represents the lateral pressure coefficient.